The present invention relates to a rear viewer for automobile which enables an automobile driver to see condition at a road immediate behind and below rear end portion of his automobile.
Heretofore, the inventor has invented and filed various rear viewers for automobile. An example thereof is a rear viewer as shown in FIG. 1 wherein a holder frame box 2 of a triangular cross section has a thin plate-like Fresnel concave lens F mounted on an opening at its under side, a flat plate-like reflex mirrow M.sub.1 mounted on inner side of its inclined roof and a front side having an opening. The holder frame box 2 is bonded on the outer surface of a rear window glass of an automobile at the front side of the holder frame box 2 (as shown in U.S. Pat. No. 4,274,714). Another example is a rear viewer as shown in FIG. 2 wherein a holder frame box 2 has an inserted and bonded transparent plate having a surface of a plate-like prism P and an opposite surface of a plate-like Fresnel concave lens surface F at inclined opening on rear edge of the holder frame box 2 and the front edge of the holder frame box 2 is bonded on an outer surface of a rear window glass 1 of an automobile (as shown in Japanese Utility Model Application Laid Open Publication No. 28,041/82). Thirdly, FIG. 3 shows an example of conventional rear viewers wherein peripheral edge of a convex reflex mirror M.sub.3 is bonded on a holder plate H which adjustably holds a tip ball of a support arm T protruded from an attaching hole on rear upper portion of an automobile body B.
The above three examples of conventional rear viewer will be scrutinized from optical view points as follows. In the rear viewer shown in FIG. 1, condition at a road over a desired distance from a point b immediate behind and below the rear end portion of the automobile to a point a of a desired rearward distance (as shown by an arrow from point b to point a) is reflected by the plate-like reflex mirror M.sub.1 through the plate-like Fresnel concave lens F to the automobile driver to give an invert state of image at the road as shown by an arrow from a point b" to a point a". Namely, the automobile driver has to see the point b immediate behind and below the rear end portion of his automobile as an upper position and the rearward point b as a lower position, so that the automobile driver has to see condition at a road immediate behind and below the rear end portion of the automobile by only an invert state of image (refer to FIG. 7).
In the rear viewer shown in FIG. 2, angle of depression Q of the lens is 60.degree. with respect to horizontal line. At the present stage of technique, angle of depression Q of a lens is about 60.degree. at the maximum due to various optical restrictions such as material of the lens and shape of the lens etc. Thus, the part from a point b to a point c corresponding to an angle S, i.e., 30.degree. with respect to the vertical line, can not be seen by the automobile driver at all. As a result, the automobile driver can not see or ascertain condition at a road immediate behind and below the rear end portion of the automobile, even though he can see the part behind the point b as a normal state of image.
In the rear viewer shown in FIG. 3, condition at a road immediate behind and below rear end portion of an automobile can be seen at any rate by the automobile driver as an invert state of image similarly as in FIG. 1. However, since the rear viewer of this type gives a reflected image by means of a convex mirror, the automobile driver can see only a distorted image and the rear end portion of the automobile has to be bored for receiving an arm which supports the rear viewer. That is, as shown in FIG. 3, since the rear window is disposed to outer air atmosphere and the mirror is provided at the position apart from said rear window and projected outwardly, there is a disadvantage that the rear window has to provide at least one of defroster and rear wiper, etc., even though said mirror is provided toward downward direction. These are a further disadvantage in addition to the former disadvantageous optical property.